The specificity of antibody-independent immunity elicited in B cell deficient mice by acute infection with P. chabaudi will be investigated. Mice will be rendered B cell deficient by treatment with goat anti-mouse IgM initiated on the first day of life. Mice lacking IgM will be immunized at 6 to 10 weeks of age by infection with P. chabaudi. Subsequently, immunized mice will be tested for their ability to resist challenge with both homologous and heterologous hemoprotozoa. Also, having shown that antibody-independent immunity to malaria can be transferred with spleen cells, we will attempt to identify the cells responsible. This will be accomplished by cell transfer of lymphocyte preparations enriched for either T or B lymphocytes, into B cell deficient mice. Subsequently the recipients will be challenged with P. chabaudi. Subpopulations of lymphocytes involved will be determined by deletion studies utilizing appropriate reagents.